Presence functionality in the H.323 protocol

ABSTRACT

A Present Application Server (PAS) is holding a presence list for each user is introduced. The presence list of a first user comprises other network registered users for which the first user, wants to track the registration status. The registration status of each user corresponds to the user&#39;s registration status in their associated Gatekeepers. Each time a change in registration status for a user occurs in its associated Gatekeeper, the Gatekeeper will send a message including an identification of both the user and the Gatekeeper, in addition to information concerning the change of status (register or unregister). The presence lists affected by the change of the registration status of said user is updated in the PAS. Then the associated users are informed by messages sent from the PAS via the Gatekeeper to the user&#39;s EndPoints. The messages are adapted to refresh URL&#39;s at the EndPoints pointing at the user&#39;s presence list.

FIELD OF THE INVENTION

The present invention is related to packet-based multimediacommunication systems, especially presence functionality related to theH.323 protocol.

BACKGROUND OF THE INVENTION

Presence and chat applications (e.g. ICQ on the Internet) are gainingpopularity. These applications are based on that the users registertheir presence and may be visible on other users contact or buddy lists.An example of such an application is ICQ. ICQ is a presence and chatservice on the Internet. ICQ allows you to know which of your friendsthat are online, and you may use a variety of communication techniquesto contact them. It is also integrated with Microsoft NetMeeting.

This is for the time being the most common application, but otherpresence applications are expected to be common in the near future. Anexample of such an application is a localization application by which agroup of users are informed e.g. via a map on a terminal screen wherethe other users currently are positioned. The positions may be providedby a GPS receiver placed in each user's terminal. Especially this lastmentioned application or similar applications are expected to becomepopular services, and therefore, presence application will probablyoccur in an increasing number of associations.

As also IP telephony becomes more customary, it is clear that there is aneed for solutions implementing presence applications therein. H.323 istoday one of the most widespread protocol for IP telephony or moregenerally for multimedia communication where the underlying transport isa Packet Based Network. The description in this application is appliedto this protocol, and associated terminology, well known to personsskilled in the art, will be used.

According to the H.323 standard, user registration into a network isarranged by so-called Gatekeepers.

The H.323 protocol describes/provides the procedure for the userregistration. The user registration is basically a relation between theuser identifiers (called aliases in H.323) e.g. E.164 numbers or e-mailaddresses and the users current IP address. See FIG. 1.

When a User A registers into the H.323 based system, its endpoint,representing the users terminal, sends the information about the IPaddress associated with that endpoint. This information is encapsulatedin a registration request message (RRQ) and sent to a H323 Gatekeeper(GK) (1). The relevant information from the RRQ message is then storedin a dB (2). As an acknowledgement to the user about its registration,the GK responds with a registration confirmation message (RCF), (3).This is a normal registering procedure in H.323 based systems.

The User A is now recognised within the system under aliases E164: 523946, e-mail: userA@ipt.com and can be contacted on IP:111.12.11.17.

H.323 is based on users registering into a network, but there iscurrently no way to provide the already existing registration status(presence) to other users in the H.323. Consequently, there is currentlyno way other users can find out if User A is registered or not, and UserA can not notify his friends about his/hers presence in the system usingH.323.

ICQ is a presence and chat service on the Internet. ICQ allows you toknow which of your friends that are online, and you may use a variety ofcommunication techniques to contact them. It is also integrated withMicrosoft NetMeeting, which in fact is a H.323 endpoint.

However, if you want to be registered into a H.323 network, you wouldhave to register both in ICQ and the H.323 network, and you will notknow if other users registered in ICQ also are registered in a H.323network. ICQ does not make use of the information already stored in theGatekeepers whether a user is logged in or not.

SIP is another protocol that may be used for IP telephony. SIP, likeH.323, uses registrations to map user identifiers to host names andthereby IP addresses. SIP has proposed extensions for presence handling.The mechanism is based on that a user may send a SUBSCRIBE message tosubscribe to other users registrations, and will get a NOTIFY messagewhen one of these users changes his/her registration status.

However, this is a mechanism for SIP protocol, and is not applicable forequipment using the H.323 protocol. Therefore, none of the abovementioned known solutions solve the problem of relating presenceinformation to registration status in an H.323 network.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method thateliminates the drawbacks described above. The features defined in theclaims enclosed characterize this method.

More specifically, the present invention introduces a PresentApplication Server (PAS) holding a presence list for each user. Thepresence list of a first user comprises other network registered usersfor which the first user, according to a predefined request list storedin the PAS, wants to track the registration status. However, accordingto a preferred embodiment of the present invention, a second user, nothaving the first user in an associated trust list, will not be includedin the presence list of the first user even if the second user both isregistered in the communication network and included in the request listof the first user.

The present invention is applied to the H.323 standard, and theregistration status of each user corresponds to the user's registrationstatus in their associated Gatekeepers. Each time a change inregistration status for a user occur in its associated Gatekeeper, theGatekeeper will send a message including an identification of both theuser and the Gatekeeper, in addition to information concerning thechange of status (register or unregister). As a response to this, thepresence lists affected by the change of the registration status of saiduser is updated in the PAS. Then the associated users are informed bymessages sent from the PAS via the Gatekeeper to the user's EndPoints.The messages are adapted to refresh URL's at the EndPoints pointing atthe user's presence list.

The present invention make use of the registration status informationalready stored in the Gatekeepers. Then the users may be visible forother users in a presence application just as they are attached to aGatekeeper.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to make the invention more readily understandable, thediscussion that follows will refer to the accompanying drawings.

FIG. 1 shows a normal registration procedure in an H.323 based system.

FIG. 2 is an overview of the system concept according to the presentinvention

FIG. 3 shows the relationship between an H.323 Gate Keeper and thePresence Application Server (PAS) according to the present invention.

FIG. 4 shows a registration procedure in an H.323 based system usingAnnex K according to the present invention.

DETAILED DESCRIPTION

The present invention introduces a Presence Application Server (PAS)communicating with one or more Gatekeepers. The PAS (PresenceApplication Server) is handling presence services. It is separated fromthe gatekeeper to make the system scalable. This is shown in FIG. 2. Bydoing this, the PAS may be shared by many gatekeepers, even gatekeepersbelonging to different H.323 operators.

According to the present invention, a User 1 will have both a requestlist and a trusted list in the PAS. The request list contains all theusers for which User 1 wants registration status. The trusted listcontains all the users that User 1 allows to be notified when his/herregistration status changes.

The PAS has to correlate these lists with registration status andthereby make one presence list for User 1 containing the currentlyregistered users included in the request list of User 1. A user in thepresence list of User 1 also have to have User 1 included in its trustedlist. If not, the user will be excluded from the presence list of User 1even if it is both registered and included in the request list of User1.

This may be exemplified by the following tables including the requestlists and trust lists of User 1, User 2, User 3 and User 4,respectively.

User Registered Request List Trust List User 1 GK A User 2, User 3, User4 User 2, User 3 User 2 No User 1, User 3 User 1, User 3 User 3 GK BUser 1, User 2, User 4 User 1, User 2, User 4 User 4 GK B User 1, User 3User 3

The PAS will in this case have the following compiled presence lists forthe users:

User Presence List User 1 User 3 User 2 Not registered User 3 User 1,User 4 User 4 User 3

The connection between the GK and the PAS is structured with the PAS asa server and the GK as a client. Initially the GK may be pre-registeredat the PAS. The protocol used between the GK and the PAS, may be a“presence protocol” (PP), which is known for persons skilled in the art,and has the following characteristics:

-   -   The GK may be pre-registered at the PAS.    -   Provides a communication between the GK and PAS.    -   The GK sends messages related to user registrations to the PAS.    -   The PAS sends events related to user presence information to the        GK's.

The messages sent to the PAS includes one or more user IDs, the ID ofthe corresponding GK and the operation: register or unregister. Theevents sent from PAS to GK's contain user ID and a presence information.FIG. 3 shows the relationship between the GK and the PAS.

As earlier mentioned, PP is the interface between the H.323 GK and thePAS. This protocol could be part of a standard service API like Parlay,an extension to H.323, XML based or based on other applicable protocols.The exact syntax and transport mechanism for this protocol is outsidethe scope of this invention.

The PP interface consist of the following components:

RegistrationInfo. Info sent by the client (GK). This info contains auser ID, GK ID with an operation: register or unregister.

RegistrationInfoAck. A response to RegistrationInfo containing presenceinformation for the registered user.

PresenceNotification. The event could be triggered by PAS when aRegistrationInfo message is received. This event contains a user ID andpresence information.

According to a preferred embodiment, the present invention is realizedby using H.323 Annex K. Annex K describes a service independent HTTPbased transport channel where H.323 messages are used for transportingthe URL for the services.

Realisation of a presence service based on Annex K is shown on FIG. 4.Given that the user A has received an URL from its service provider.

During the registration procedure, the terminal of user A sends a RRQmessage to user A's GK, (1). Parts of the registration information isencapsulated in a RegistrationInfo message and sent to the PAS, (2). ThePAS returns an URL pointing to User A's compiled presence list to theuser's GK in RegistrationlnfoAck (3). The gatekeeper will then includethis URL in the ServiceControlSession structure in the RCF (4).

At the same time the PAS will send notifications to all users that aresubscribing to registration events for User A. This is done by sending aPresenceNotification to the gatekeepers of these users in which a URLpointing to an updated presence list (5) for each of these users isincluded.

The gatekeepers will in turn send a ServiceControlIndication message tothe users endpoints (6), which will display/refresh the URL to get thelatest presence information.

Unregistration is handled in a similar way. The RegistrationInfomessages will have status unreg instead of reg, and no URL will bereturned in RegistrationInfoAck. (5) and (6) will be the same.

The present invention in the H.323 system is a supplement to alreadyexisting registration functionality. The registration functionality isextended with additional services allowing the user to be provided withinformation about the current registration of his/hers friends and to“publish” information about own registration.

The present invention make use of the registration status informationalready stored in the Gatekeepers. Then the users may be visible forother users in a presence application just as they are attached to aGatekeeper.

The invention is also applicable in conjunction with locationfunctionality. The additional information about users physical locationin terms of e.g. GPS (Global Positioning System) co-ordinates could betransferred to the PAS, assuming that the user terminal supports GPS.

In fact, there are no restrictions in what kind of information thatmight be attached to each user in the presence list.

Finally, according to the present invention, it should be possible tolet the same PAS also handle presence information from others than H.323users, e.g. SIP users.

REFERENCES

-   ITU-T Recommendation H.323, Packet-Based Multimedia Communications    Systems, version 4.-   ICQ (http://web.icq.com/)-   M. Handley/H. Schulzrinne/E. Schooler/J. Rosenberg, “SIP: Session    Initiation Protocol”, RFC 2543, IETF; March 1999.-   J. Rosenberg et. al., “SIP Extensions for Presence”,    <draft-rosenberg-impp-presence-00.txt>, IETF; June 2000. Work in    progress-   A. Roach, “Event Notification in SIP”,    <draft-roach-sip-subscribe-notify-03.txt>, IETF; February 2001. Work    in progress.-   H.323 Annex K (HTTP based service Control Transport Channel)

1. A method for tracking a registration status of one or more users in acommunication network according to H.323 or SIP standard, said usersassociated to a Gatekeeper (GK) administrating registrations andunregistrations of said users, each user accessing the communicationnetwork through an associated EndPoint of the communication network, themethod comprising: sending a first message from said Gatekeeper to aPresence Application Server (PAS) which holds a presence list for eachof the users for tracking user registration status, each time one of theusers changes registration status in the communication network, whereina first user is included in a presence list corresponding to a seconduser, said first message includes a user identification of the currentuser, a Gatekeeper identification, and the change of registration statusfor said user, returning, from said PAS to said GK, a URL pointing tothe presence list of said user, updating presence lists affected by thechange of the registration status of said user accordingly, sending,from said PAS, a second message to the Gatekeeper notifying theGatekeeper about the updating.
 2. The method according to claim 1,wherein the first user is included in the presence list corresponding toa second user if all of the following three criteria are fulfilled: thefirst user is registered, through the Gatekeeper, in the communicationnetwork; the first user is included in a request list corresponding tothe second user; and the second user is included in a trust listcorresponding to the first user.
 3. The method according to claim 2,wherein said request list corresponding to the second user is apredefined list including all users for whom the second user wants totrack the registration status.
 4. The method according to claim 3wherein said trust list corresponding to the first user is a predefinedlist including all users that the first user allows to be notified whenthe first user changes registration status.
 5. The method according toclaim 4 wherein communication between the PAS and the Gatekeeper iscarried through by means of a Presence Protocol (PP) wherein the PASacts as a server and each GK as a client.
 6. The method according toclaim 5 wherein the step of sending the second message precedes sendinga third message from the Gatekeeper to the users whose presence listshave been updated, said third message adapted to refresh a URL,localized in each of those user's EndPoints pointing to the associatedpresence list.
 7. A Presence Application Server (PAS) for tracking aregistration status of one or more users in a communication networkaccording to H.323 or SIP standard, said users associated to aGatekeeper (GK) administrating registrations and unregistrations of saidone or more users, each user accessing the communication network throughan associated EndPoint of the communication network, the PAS comprising:means for communicating with the GK, the PAS receiving a first messageindicating change in registration status of a first user, the firstmessage including a user identification of a user, a GK identificationand change of registration of the user; means for storing a presencelist for each user subscribing to a presence service associated with thePAS, wherein a first user is included in a presence list correspondingto a second user; means for sending to the GK a URL that points to thepresence list of the subscribing user; means for updating the presencelist of each user according to registrations and unregistrations of eachof the users into or from the communication network that utilize theGatekeeper.